As conventional materials of contact and terminal parts, such as connectors and switches, there are used plated products wherein a base material of copper, a copper alloy, stainless steel or the like, which is relatively inexpensive and which has excellent corrosion resistance, mechanical characteristics and so forth, is plated with tin, silver, gold or the like in accordance with required characteristics, such as electrical and soldering characteristics.
Tin-plated products obtained by plating a base material of copper, a copper alloy, stainless steel or the like, with tin are inexpensive, but they do not have good corrosion resistance in a high-temperature environment. Gold-plated products obtained by plating such a base material with gold have excellent corrosion resistance and high reliability, but the costs thereof are high. On the other hand, silver-plated products obtained by plating such a base material with silver are inexpensive in comparison with gold-plated products and have excellent corrosion resistance in comparison with tin-plated products.
The materials of contact and terminal parts, such as connectors and switches, are required to have good wear resistance against the insertion and extraction of connectors or the sliding movements of switches.
However, in silver-plated products, there is a problem in that the crystal grains of the silver plating film are easily increased by recrystallization, the increase of the crystal grains decreasing the hardness of the silver plating film to deteriorate the wear resistance thereof (see, e.g., Japanese Patent Laid-Open No. 2008-169408).
As a method for improving the wear resistance of such silver-plated products, there is known a method for improving the hardness of a silver-plated product by causing an element, such as antimony, to be contained in the silver plating film (see, e.g., Japanese Patent Laid-Open No. 2009-79250).
However, if an element, such as antimony, is contained in the silver plating film, there is a problem in that the contact resistance of the silver plating film is increased since the purity of silver is lowered although silver is alloyed to improve the hardness of the silver plating film.